GRAPHIC EQUALIZERTOA 1000 series

E-1231

Operating Instructions

CAUTIONTO REDUCE THE RISK OF ELECTRICAL

SHOCK, DO NOT REMOVE COVER.

NO USER SERVICEABLE PARTS INSIDE.

REFER SERVICING TO QUALIFIED

SERVICE PERSONNEL.

THE LIGHTNING FLASH WITH

ARROWHEAD WITHIN A TRIANGLE IS

INTENDED TO TELL THE USER THAT

PARTS INSIDE THE PRODUCT ARE A

RISK OF ELECTRIC SHOCK TO

PERSONS.

THE EXCLAMATION POINT WITHIN A

TRIANGLE IS INTENDED TO TELL THE

USER THAT IMPORTANT OPERATING

AND SERVICING INSTRUCTIONS ARE

IN THE PAPERS WITH THE

APPLIANCE.

Please follow the instructions in this manual to obtain the optimum results from this unit.We also recommend that you keep this manual handy for future reference.

TOA Corporation

Contents

Cautions

General Description

Features

Front Panel

Rear Panel

Input/Output Connections

Installation Precautions

Applications

Optional Matching Transformer Mounting

Performance Graphs

Block Diagram

Specifications

Accessories

Appearance

2

3

3

4

5

6

6

7 • 8

9

10

11

12

12

12

Cautions

1. Do not operate the E-1231 from power mains which exceeds the indicatedmains voltage by more than 10%.

2. Do not expose the E-1231 to corrosive chemicals or liquids such as softdrinks, salt water, etc.

3. Always refer the E-1231 to qualified technical service personnel.

— 2 —

General Description

The E-1231 is a single channel, 1/3 octave active graphic equalizer designed toallow clean, accurate audio equalization for stage, studio, or commercialapplications.

The E-1231 provides 12dB of boost or cut at each of its 28 frequencies, whichare centered at ISO 1/3 octave increments from 31.5Hz to 16kHz.

The E-1231's active bandpass/bandreject filters are designed for minimumphase shift, and feature smooth slide controls with center detents for easy andaccurate adjustment. (The filters are summed in parallel for reliability, so thatthe failure of one filter does not interrupt operation of the others.)

In addition, continuously variable highpass filters are provided on the frontpanel. The highpass filter has a slope of 12dB per octave and is variable from15Hz to 300Hz, while the lowpass filter can set for either a 6dB per octaveslope or a 12dB per octave slope and is variable from 2.5kHz to 30kHz.

An input level control on the E-1231 gives ±12dB of adjustment to allow a widevariety of input sources. A LED indicator illuminates when either the input or theoutput comes within 3dB of clipping. In addition to the usual EQ in/out switch,an automatic EQ bypass function provides complete equalization bypass in theevent of loss of AC power, and an output muting function suppresses turn-on/turn-off transients.

A security cover is included with the E-1231 to guard against accidentaldisturbance, or intentional tampering when used in fixed installations.

The E-1231 can be mounted in a standard 19" rack and occupies 3-1/2" ofvertical space.

Features

1. 28 filters on ISO 1/3 octave center fre-quencies from 31.5Hz to 16kHz.

2. 12dB boost or cut at each center frequen-cy, continuously variable.

3. High quality, low phase-shift active filters.

4. Precision calibrated, noiseless slide con-trols with center detent.

5. Equalizer In/Out switch.

6. Continuously variable highpass and low-pass filters.

7. LED peak indicator to detect clipping atinput or output levels.

8. Variable input level control to accept varie-ty of input sources.

9. Automatic EQ bypass circuitry.

10. A security cover is included.

11. Filter In/Out switch

12. Lowpass filter can be set for either6dB/oct or 12dB/oct.

13. Optional input/output transformers thatconvert electronically balanced input/out-put to transformer balanced input/output.

— 3 —

Front Panel

Lowpass Filter Slope Selection SwitchThis switch sets the lowpass filter's per octave attenuation for either 6dB or 12dB.

Peak Indicator LEDThe peak indicator LED lights when either the input or the output level reaches 3 dB below clipping.

Input Level ControlThis control adjusts the input gain by ±12dB to allow the use of a wide range of input sources. Toinsure the best S/N ratio possible, adjust this control so that the peak LED flashes only occasionally.

Lowpass Filter ControlThis is a shelving-type filter that provides a 12dB or 6dB per octave roll off above 2.5kHz and up to30kHz. Its main purpose is to stop high frequency noise, oscillation, and certain types of RFinterference from damaging tweeters. It is also useful in reducing excessive background noise, suchas that produced by old phonograph records.

Equalizer SlidersThese sliders are adjusted to tune or equalized the overall frequency response of a sound system.

Equalizer Indicator LEDThe indicator LED turns on whenever the equalizer IN/OUT switch is "in".

Equalizer IN/OUT SwitchEqualizer switch puts the input signals either in circuit or out of circuit of the equalizer. The "out"position provides flat audio response no matter what the positions of the equalizer sliders and thefilter (LPF/HPF) control.

Security Cover Mounting HoleThis hole is used to mount the supplied security cover with two screws to avoid accidental changesin set position of control knobs and switches.

Power SwitchPushbutton alternately switches the AC power on and off.

Power Indicator LEDThe green LED lights when the power switch is "on".

Highpass Filter ControlThis shelving-type filter provides an 12dB per octave rolloff between 300Hz and 15Hz. It is especiallyuseful for reducing stage or turntable rumble, AC hum, wind noise, and other subsonic componentsthat waste amplifier power and tax speakers.

Filter Indicator LEDThe filter indicator LED lights when the filter switch is "in".

Filter IN/OUT SwitchPressing this switch while equalizer indicator lights provides the frequency response set for by thelowpass- and highpass-filter control. Press the switch again to disable the lowpass- and highpass-filter control.

— 4 —

Rear Panel

AC Fuse HolderWhen replacing, be sure to use the fuse of specified rating and type to avoid the possibility of fire.

Fuse rating220-240V version 250V T80mA120V version 250V 0.2A

AC Power Cord

Ground Screw TerminalHum can result from a ground loop to be formed when the E-1231 is connected to other equipment.In such cases, cut the loop by removing a short piece, which should usually be mounted to theterminal.

Output Screw TerminalThe output terminal is balanced and 600 ohms in output impedance. Place the supplied short piecebetween E and C to convert to unbalanced type.

Input Screw TerminalThe input terminal is balanced and 10k ohms in input impedance. Place the supplied short piecebetween E and C to convert to unbalanced type.

— 5 —

Input/Output Connections

Input terminal from mixer, etc.

Input terminal from mixer, etc.

E-1231

E-1231

Power Amplifier

Speaker System

Installation PrecautionsGround LoopsIn any audio system, there are numerous ways by which ground loops can be created.For example, they may occur when the E-1231 is mounted in a rack cabinet, orthrough AC ground when the E-1231 connected with preamps, mixers, etc. Theseground loops may cause hum and noise if care is not taken during connection. Anincrease in noise from ground loops may be minimized by breaking the ground loop.Generally, the chassis ground of the signal line should be broken as shown below.

When hum is generated from a ground loop, detach a short piece from the groundscrew terminal.

— 6 —

Applications

Feedback PreventionWhen the overall gain of a sound system is increased,feedback will occur at frequencies where the systemresponse has peaks. Suppose the system has anuneven frequency response like that shown in thefollowing diagram. The frequency at which feedbackwill occur when gain is increased is about 500Hz. Inthis case, feedback may be prevented by attenuating

levels at 500Hz by 3dB to 5dB with the E-1231. If theoverall gain is again gradually increased, feedback willoccur next at about 125Hz. It may be stopped byattenuating the levels 2dB to 3dB at that frequency. Inthis procedure, sufficient gain in the sound system isobtained before feedback.

Sou

nd P

ress

ure

Leve

l

FrequencyRoom EqualizationIn a sound reinfocement system for a room, the clarityof sound can be adversely affected by the roomfrequency response including standing waves (roomresonances), reflections of sound, and relationsbetween direct and indirect sound.The E-1231 is an effective tool to equalize the roomfrequency response to a flat response and improve

sound clarity.For example, suppose that there is a room frequencyresponse as shown below.The equalizer sliders are set as shown below.The overall response after equalizationwill then be as follows.

Sou

nd P

ress

ure

Leve

l

Frequency

The equalizer sliders are set as shown below.

The overall response after equalization will then be as follows.

Sou

nd P

ress

ure

Leve

l

Frequency

Before equalizationFrequency responseof equalizer

Frequency responseafter equalization

— 7 —

ApplicationsEqualization for musicThe Graphic Equalizer is designed not only for use in preventing feedback andequalizing uneven room frequency response to be flat, but also for equalizingfrequency response to your tastes and producing favorable sound for you. Fig.1 showseach frequency band and its corresponding auditory feeling. Fig.2 and Table 1 showthe relation between each musical instrument and its frequency band. They can be ofgreat help in the equalizer operation. (They are referenced from a book entitled"Practical Guide for concert")

EQUALIZATION CHART

These soundsare felt morethan reallyheard. Theygive a senseof power.Too muchproduces amuddy sound.

The rhythm sec-tion appearshere. Either a fator thin soundcan be heard bymis-EQ here. Toomuch becomesboomy. Bass gui-tar-Snare-Toms.

Probably the most im-portant of all. Most allinstruments containharmonics here. 300 Hzboosting can cause hornlike sounds. 1 k to 2 ksounds tinny. Too muchhere sounds like the tel-ephone.

Upper vocal region.Too much here willcause great fatigue,and loose speech in-telligence. Reducing3 k can bring vocalson top.

Presence range.Great achievementin overall level canbe had here. Toolittle causes a "faraway" sound.

Sibilancelevels can becontrolledhere. Bright,clean defini-tion.

Fig.1

INSTRUMENT CHART

Fig.2

INSTRUMENT EQUALIZATION CHART Table 1Acoustic guitarBass strings resonate between 70 to 120Hz, body around 300Hz.Avoid boosting these to stop feedback. 3kHz and 5kHz givesgreat "clarity".Electric guitarResonances differ-depending on type. Good full sounds around300 to 500Hz. Clarity at 3kHz.Bass guitarExtreme lows are at 60 to 90Hz. "Pick" or "pluck" sounds arearound 800 to 1200Hz. Upper harmonics clarified about 3kHz.Human voiceGood fullness at 150Hz. Watch for "boominess" around 250Hz.Mid-range 10kHz.Piano (Acoustic)Bass strings responate around 100Hz. Watch for subharmonics at30 to 50Hz.Piano (Electric)Good mid-clarity at 3kHz to 5kHz thins out rapidly in high end. Becareful around 1.5kHz to 2.5kHz to avoid the "bar room sound".OrganUsually dies under 200Hz. Has great mid-sounds around 1200 to2000Hz. Top end cuts off at 6kHz.ViolinRichfullness at 400Hz. Natural mids around 1500 to 2500Hz. Avoid"scratch" sounds at 8kHz.Brass instrumentsWatch for "hot" mids around 2kHz. Low end boost around 400Hz.Top end clarity at 6kHz.Bass drumGreat low "kick" at 40Hz. The mids at 2kHz gives the familiar"punch".Snare drumGood fullness at 100Hz. The "crack" is boosted at 2kHz. Realeasy. The snares extend to above 4kHz.Tom TomThe main fullness is around 200Hz. The mid punch extends to4kHz.Floor TomSame as tom, but extends down to 80Hz.Hi HatWatch for the "gong" sound around 300Hz. Good "shimmer"sounds are around 8kHz to 10kHz.Cymbal overheadAbout the same as hi-hat only has more low end around 150Hz.Talk BoxDepending on the guitar sound driving it and the resonance ofeach player's mouth, should have great "bite" around 1200Hz anddies above 6kHz.

— 8 —

Optional Matching Transformer Mounting

[CAUTION]THESE SERVICING INSTRUCTIONS ARE FOR USE BY QUALIFIED PERSONNEL ONLY.TO AVOID ELECTRIC SHOCK DO NOT PERFORM ANY SERVICING OTHER THANTHAT CONTAINED IN THE OPERATING INSTRUCTIONS UNLESS YOU AREQUALIFIED TO DO SO. REFER ALL SERVICING TO QUALIFIED SERVICE PERSONNEL.

The E-1231's input and output are electronically balanced. These can be converted totransformer balanced input and output using the optional matching transformer LT-101(input) and LT-102 (output).

1. Set the power switch to OFF and unplug the AC cord form a wall outlet.

2. Remove the case by loosening six side panel screws (three each on each side)and two rear panel screws.

3. Install sleeves (supplied with the transformer) by tightening screws from the otherside of a chassis, and mount the transformer to the sleeves using screws. See Fig.1.The input transformer must be located on the left and the output transformer onthe right.

4. When mounting the input transformer, detach connector from CN-104, reconnectthe detached connector to connector at the transformer side, and then connectconnector from the transformer to CN104.When mounting the output transformer, detach connector from CN-103,

connector at the transformer side, and thenconnector from the transformer to CN103.

reconnect the detached connector to

See Fig.1.connect

Fig.1

5. Fit the case in place.

Transformer Specifications

Model

Frequency response

Constant loss

Distortion

LT-101

30Hz ~ 20kHz(at ±0.15dB)

Within 1.5dB(at 1kHz)

Less than 0.2%(50Hz/5dB)

LT-102

30Hz ~ 20kHz(at ±0.15dB)

Within 1.5dB(at 1kHz)

Less than 0.2%(50Hz/5dB)

0dB = 0.775V RMS

Specifications are subject to change without notice.

— 9 —

Performance Graphs

Frequency Response(Each slider is set at a max or min position) Frequency Response (ex. 800Hz slider)

Frequency Response (ex. 630Hz, 800Hz, 1kHz slider) High pass Filter

Low pass Filter

— 10 —

Block Diagram

— 11 —

SpecificationsFrequency Response

±1dB, 20Hz to 20kHzTotal Harmonic Distortion

Less than 0.01% at 1 kHz, all sliders at 0 position,rated output

Equalization Center Frequencies31.5Hz to 16kHz31.5Hz, 40Hz, 50Hz, 63Hz, 80Hz, 100Hz, 125Hz,160Hz, 200Hz, 250Hz, 315Hz, 400Hz, 500Hz, 630Hz,

4kHz, 5kHz, 6.3kHz, 8kHz, 10kHz, 12.5kHz, 16kHzRated Input Level

+ 4dB (INPUT LEVEL CONTROL set for 0 position)Rated Output Level

+ 4dB with 600-ohm loadMaximum Input Level

+ 20dB at 1kHzMaximum Output Level

+ 20dB with 600-ohm loadInput Impedance

10k ohmsOutput Impedance

600 ohmsHum and Noise

—94dB (EQ in, all sliders at 0 position, 20~20kHzBPF)

IndicatorsA red LED for output and input clipping, A greenLED for equalizer IN, A green LED for power ON, Agreen LED for filter IN

ControlsEqualizer Sliders

±12dBInput Level Control

±12dBHighpass Filter

12dB per octaveAdjustable Cutoff Frequency:15Hz to 300Hz

Lowpass Filter12dB per octave/6dB per octaveAdjustable Cutoff Frequency:2.5kHz to 30kHz

AC Line VoltageAC mains, 50Hz/60Hz

Power Consumption11 watts

FinishBlack

Dimensions(W X H x D)483 x 88 x 317mm(19.0" x 3.5" x 12.5" )

Weight4.5kg (9.9lbs.)

Note:0 dB is referenced to 0.775 volts RMS.Specifications are subject to change without notice.

Accessories

Security coverScrew for security coverShort piece

122

FuseWarranty card (for USA and Canada)Operating instructions

111

Appearance

mm(inch)

TOA CorporationKOBE, JAPAN

Printed Japan133-12-037-2A

— 12 —